(1) Field of the Invention
The present invention relates to an improved process for removing pollutants, especially sulphur dioxide and nitrogen oxides, from effluent gases resulting from various chemical processes and by the combustion of carbonaceous fuels. This invention relates to treating effluent gases so that these pollutants may be changed into particle form or mist form, thereby enabling collection of the particles or mist pollutants by conventional collecting means such as precipitators, filters and the like. Specifically, the invention relates to the combination of corona discharge treatment with previous processes known to provide for the removal of sulphur dioxide and nitrogen oxide from such fuels.
(2) Description of the Prior Art
The need to deal with the deleterious effects of emissions generated from various sources such as industrial processes and energy production of various kinds is well known. The impact of such emissions on human health has recently been the subject of intense study and public debate, and legislative action to mandate safer emissions has already been taken and will probably be enlarged or extended in the future. The "acid rain" controversy has, of late, focussed the public's attention on the effects of such emissions on the natural environment and promises to provide a continuing debate over the causes of water pollution and appropriate legislative action that should be taken to curtail such pollution. The main emissions identified as having such adverse effects are various forms of nitrogen oxides (NO.sub.x) and sulphur dioxide (SO.sub.2). Other byproducts of the energy creation process such as particulates are of less concern since known (albeit expensive) methods are available for their removal.
Each of the above problems forces the public to choose between the present and relatively cheap methods for producing energy and chemicals on the one hand, and increasing the cost of such production and processes by either changing to a different energy production process or altering current processes by the addition of equipment designed to remove such pollutants.
In response to the above, several methods and apparatus have been developed to minimize the sulphur dioxide pollution caused by the burning of carbon fuels. Typically, such methods and apparatus are costly and have large operating and maintenance problems.
The prior art has included various methods for removing the above noted contaminants from the energy production process. One such technique is referred to as the spray drying process. In the spray drying process, a mixture of water and alkali reagent such as lime is injected into the stream of effluent gases in a reaction chamber resulting in the formation of solid products from the reaction between the reagent and the pollutants. From the chamber the effluent gases pass into a particulate collection means such as a fabric or bag filter or an electrostatic precipitator whereat the solid particles of the reaction between the reagent and the pollutants are removed. The purified effluent gases are passed into a stack from which they are discharged after passing through the particulate collection means.
In order to operate the spray drying process most efficiently, large amounts of alkali reagent are needed, but such large amounts of reagent require correspondingly large amounts of water to operate properly. For this reason methods for increasing the efficiency of the spray drying process which do not require the use of additional amounts of reagent are desirable.
Another type of prior art pollution control system utilizes radiation in various forms to improve the efficiency of the process. Such systems use electron beam or ultraviolet light to oxidize the nitrogen oxides and sulphur dioxides in the effluent gases. The ionization caused by the electron beam irradiation converts the sulphur dioxide and nitrogen oxides to acid mist at low temperatures and/or solid particles at high temperatures (in the presence of ammonia) which latter byproducts are removed in a conventional manner for later disposition. In the electron beam method, costly and elaborate shielding measures must be employed.